Aiming at the reliability of thin-film thermocouples applied to turbine blades at high temperatures, combined with high-temperature tests and finite element analysis, this paper studies its failure mechanism and thermal stress under thermal load. Multi-layer thin-film thermocouple samples were prepared on ceramic substrate, and high-temperature tests were carried out under different temperature loads, and the phenomenon of film shedding and cracking was observed using electron microscope. This paper analyzes the failure mechanism of the film sensor based on the function and structure, and uses ANSYS to analyze the thermal stress distribution of the film under high temperature load. Combining several existing theoretical models, this paper analyzes the factors affecting the thermal stress of the film and conducts simulation verification.
For the thin-film thermocouple with ITO/In2O3 as the functional layer, the mechanical reliability of their composite multilayer membrane structures under high temperature and random vibration conditions are discussed. Using the elastic plasticity model based on the finite element simulation method, the stress and strain distribution patterns caused by the thermal mismatch and vibration of multilayer film materials are systematically analyzed, and the distribution of the stress concentration and strain accumulation regions that may lead to fatal reliability problems are characterized. When a thermal load of 1000 °C is applied, the protective layer of the structure is vulnerable to severe stress environment. In addition, plastic deformation occurs in the adjacent layers of the functional layer, making it a weak reliability area. The stress generated by the vibration load is much smaller than the thermal stress, which mainly occurs at the roots of the structure, where prolonged loading may lead to fatigue failure.
Molecular dynamics simulations are performed to investigate the effect of temperature on the plastic deformation mechanism in aluminum single crystal. It is found that as temperature increases the Yield strength and Young’s modulus of the aluminum under compressive and tensile strain will reduce. Moreover, it is found that the higher temperature is, the easier the dislocation emission is. Under compressive strain, the proportion of 1/6<112> Shockley type of dislocations to total dislocations is found to increase with the temperature increasing. It is also found that only a large amount of dislocation occurring incipiently the strength of the material can be yield.
As a new type of micro device, the reliability of thin film thermocouple sensor is very important in actual work. Aiming at a thin-film thermocouple sensor with NiCr as the functional layer, three main stresses of the thin-film sensor in actual work are analyzed: thermal stress, vibration stress and centrifugal stress. Various stress analyses have been verified through theoretical calculations or finite element simulations. The results show that thermal stress is the main influence stress, and the critical areas of reliability have been obtained. The prepared thin film sensor samples were tested through high temperature experiments, and the analysis results were verified. When a thermal load of 700 degrees Celsius is applied, the stress environment of the protective layer, the functional layer and the insulating layer of the structure is severe, and it is vulnerable to severe damage, and cracks are found in the insulating layer, which becomes a weak area of reliability.
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